Classification of mass movements Flashcards
Mass movement is when…
rock/earth falls/slides/flows due to gravity.
Flow is triggered when the composition…
of soil/rock is disrupted. The particles near the surface are disrupted more.
Flow is a non-
uniform movement.
(flow) Saturated topsoil results in…
lose of hydrostatic pressure and cohesion. The material eventually slips/flow.
After slip/flow, new…
deeper particles are exposed and start to lubricate.
A slide is a uniform…
movement.
During the process of formation of a slide, no internal…
disruption to rock and its properties takes place. Topsoil is disrupted.
The slide is caused by water…
sitting between the topsoil and already saturated bedrock. This creates a slip plane and the topsoil slides.
Heave is…
a very slow mass movement.
Heave is mainly occurring during…
winter.
Heave occurs on slopes with gradient…
5 degrees or more that have very little vegetation cover, which bind the soil.
Heave is caused by water…
particles in the soil, which expand as they freeze by 9 per cent.
As the water expands in the soil…
the soil is pushed 90 degrees to the slope, as it is the zone of least resistance for particles to expand.
The particles fall under a influcence of…
gravity, when the frozen water thawed and returned to its original shape.
As this freeze-thaw of water particles in soil repeats…
there is a net movement down the slope.
Rainsplash is a type of…
soil erosion caused from the impact of raindrops.
The impact of rain droplets on the soil surface often…
separate individual grains of soil moving them further from their source.
On flat surface, there is no effect of…
rainsplash erosion as the material is distributed without any net transport and particular direction.
(rain splash)On slopes, the influence of…
gravity encourages more material to be redistributed down the slope.
When slopes become steeper than…
25 degrees, almost all the redistribution occurs down the slope.
Surface wash happens when…
the soil’s infiltration capacity is exceeded.
Surface wash is common in…
winter as water drains across saturated or frozen ground and in semi-arid regions where particle size limits the infiltration.
Sheet wash is…
an unhandled flow of water over the soil.
Sheetwash usually breaks into areas of…
higher and lower velocities.
The higher velocities areas may cause…
gullying, which is the formation of narrow channel(rills)
Sheetwash may transport…
the surface regolith such as material dislodged by rain splash.
In semi-arid areas, the sheet wash can lower…
the surfaces by 2-5mm per year compared to 0.01mm on vegetated slopes.
Heave is continual…
process.
Soil creep is a slow…
movement of soil particles down the slope.
Talus creep is…
slow movement of scree fragments down the slope.
Exposed roots of three up…
slope is evidence of soil creep.
Evidence of soil creep:
Stress fractures in buildings and fractured roads/pavements
Trees react to…
the soil creep by bending the tree trunk.
Falls occur on steep slopes greater than…
40 degrees, especially on bare rock surfaces.
Initial causes of fall may be…
chemical or physical weathering, which reduces the sheer strength of the rock.
Short falls produce relatively…
straight screes-talus slopes
Talus is…
as the pile of rocks that accumulates at the base of a cliff or slope.
Longer falls produce…
a concave scar.
Falls are significant in…
producing the retreat of steep rock faces.
Slip plane of slides occurs along…
a fault line, between two different layers, a joint or a bendding plane.
Clay is particlulary vulnerable to…
the development of slip planes.
More water on the slope…
increases the water pressure and pushes particles apart, which reduces strength. It also lubricates the slope.
Slumps occur in…
a weaker rocks, especially finely weathered clays.
Slumps have a rotational…
movement along a curved slip plane.
Slumps are likely to occur when…
material becomes saturated with water and gains wight.
Often, before slumps, the base of…
the cliff is undercut by erosion(waves).
Rotational slumps are marked by…
a tilting back of the slumped mass which will expose a steep curved scar behind and pushes out a toe at the front.
Flows are more continous and less…
jerky than slumps. They have a higher water content, so more fluid.
Types of flows:
- solifluction
- debris/earth flow
- mudflow
Solifluction is the slowest…
form of flow. Around 10cm per year on the surface.
Solifluction is common in…
cold climates where frozen ground limits percolation and occur on gentle slopes (5-15 degrees).
Solifluction is formed as…
regolith becomes saturated with water. The lubricated layer then moves down the slope.
Features of the solifluction are…
lobes, which are rounded tongue like features that can be up to 50m wide.
Earth/debris flow occurs on slopes…
5-15 degrees.
Earth/debris flow is thicker than…
mudflow due to lower water content.
Earth/debris flow is caused by…
a rapid input of water from either rain or snowmelt, which causes a slippage.
Earth/debris flow leaves behind…
a concave, crescent-shaped scar and a convex lobe below.
Mudflow is similar to…
earthflow, but has thinner consistency due to high water content and it is more rapid.
Cause of mud flow is…
combination of high rainfall or snowmelt, often with impermeable rock layer beneath.
Mudflow is common in…
mountainous regions after heavy rainfall, periglacial areas ar the summer thaw maximum or on the slopes of erupting volcanoes(lahar flow).
A speed of a heave/creep is…
0.1mm to 1cm a year
A speed of solifluction is…
1cm a year to 1mm a day
A speed of landslide is…
around 1 m a day on average.
A speed of earth flow or mudflow is…
1m a day to 1m per second
A speed of debris avalanche is…
1 m/s to 360km/h
A mud/earth flow forms…
toe-fans out at the base, usually made of very fine clay.
Type of mass movements are:
- flows
- slides
- slumps
Rotational slides produce…
a series of massive steps or terraces.
Slides often occur when there is…
a combination of weak rocks, steep slopes and active undercutting.
Slides are triggered by…
change in water content or by very cold conditions.
